Trucks having open rear cargo bays are typically backed into alignment with a loading dock or other doorway of a building to facilitate loading or unloading of the truck's cargo. To protect the interiors of the building and the truck from the outside weather during loading and unloading, the space between the rear of the truck and the face of the building can be at least partially sealed off by installing either a loading dock shelter or a loading dock seal around the perimeter of the doorway
Conventional loading dock seals comprise resilient, compressible pads that are attached to the building along the top and lateral edges of the doorway. The pad compliantly conforms to the rear contour of the truck as the truck presses up against the pad, thereby sealing the gap between the face of the building and the rear of the truck.
Dock shelters typically have rigid frame members, rather than compressible pads, installed along the top and lateral edges of the doorway. The frame members usually protrude one to three feet from the outside face of the building. To avoid being struck and damaged by a truck backing into the dock, the frame members are spaced farther away from the doorway than are the compressible pads of dock seals. Flexible side curtains attached to distal edges of the frame members lie generally parallel to the face of the building and extend into the anticipated path of the truck. As a truck backs into the dock, the side and head curtains sweep across the sides and top, back corner of the truck to provide sealing between the building and the rear of the truck.
Under most conditions, dock seals and dock shelters effectively seal out weather, but in certain situations additional protection is needed. If snow, for instance, accumulates on the top of the truck while the truck is parked at the dock, warm air from inside the building may warm the truck's cargo bay. This can begin melting the snow atop the truck, which can turn the snow to slush. The liquid nature of the slush can allow it to flow back toward the loading dock. Absent an effective top seal, slush or other liquid has the potential of spilling off the trailer and into the loading dock area. The problem is worse when a sloped driveway leans the truck toward the dock. A similar runoff problem may occur with heavy rain.
To address the runoff problem, U. S. Pat. Nos. 6,233,885 and 6,550,191 disclose a roller sealing apparatus that provides a flow deflector along the roof of the truck. The apparatus includes a cylindrical roller that rides up and over the top of the truck as the truck backs into the dock. To help protect the roller from the truck's impact, the rear edge of the truck lifts the roller into position by pushing against a stiffener (175), which in turn pushes against a ramp (180). The ramp forces the roller's support (120) to move the roller up and over the truck. When resting atop the truck's roof, the roller blocks any water flowing toward the back of the truck and redirects it to drain off to either side of the truck.
Unfortunately, such a roller sealing apparatus tends to be expensive as it has to be built sturdy enough to withstand relatively high forces generated by a departing truck that includes an upwardly protruding lip along the upper rear edge of the truck. High forces can develop as the protruding lip of the departing truck catches on some edge or surface of the sealing apparatus, such as the lower edge of the ramp. Other high forces can be caused by an exceptionally tall truck backing into the dock such that the truck's upper rear edge strikes the roller sealing apparatus near the pivot point of the roller's support. In some cases, the forces may tend to lift the sealing apparatus' entire supporting framework.